1. Technical Field
The invention relates generally to annular packs for use in a wellbore.
2. Background Art
Tools requiring electrical power are often used for conducting various operations in a wellbore. This creates a need for portable electrical power, preferably power that can be mounted directly onto a downhole tool. One way of providing electrical power downhole is through the use of a battery pack. Typically, the battery pack is constructed of rigid plastic, epoxy, fiberglass, or aluminum and is mounted on or inside a downhole tool. One or more annular cells or cylindrical cells are contained within the battery pack. The cells generally are immobilized inside the battery pack by an epoxy. In order to mount or dismount the annular battery pack onto the downhole tool, the tool may have to be disassembled. Disassembly of the tool makes replacing a battery pack time consuming and, in certain cases, is impossible at the job site. For quicker job turnaround, it is desirable that the battery be removable from the tool without use of specialized equipment not available at the job site.
In general, in one aspect, an annular pack for a cylindrical member for use in a wellbore has a housing adapted to be mounted about an exterior circumference of the cylindrical member having a plurality of mutually engageable annular segments. At least one of the segments defines a chamber for housing an electrical device.
In accordance with one or more embodiments of the invention, the annular pack may have a cell for providing electrical power. The cell for providing electrical power may be shaped to match a shape of the chamber. The shape of the chamber may be cylindrical. The shape of the chamber may match a shape of the segment having that chamber. Each of the segments may have an alignment key and a cut-out for mating a respective alignment key on another segment. The segments may be electrically connected to one another when engaged. At least two of the segments may be electrically connected in parallel or series. A segment may have a plug for electrical connection to a tool. The segments may be electrically isolated from one another when engaged. The annular pack may include an electrical circuit disposed within the chamber.
In general, in one aspect, a power cell for mounting in an annular pack for providing power to a downhole tool, includes a housing having a top, bottom, and sides shaped to fit within a chamber in the annular pack, battery means for generating electricity disposed within the housing and a seal element arranged to provide a passage for electricity from the battery means through the housing.
In accordance with one or more embodiments of the invention, the power cell may include a strain relief tab within the housing for electricity connecting the battery means to the seal element. The seal element may be a glass seal integrally mounted in the cell. The power cell may include a lid, wherein the glass seal is integrally mounted in the lid. The seal element may be a glass-to-metal seal with a chamfered rim. The power cell may include a spring for biasing the battery means to one side of the housing under downhole conditions. The spring may be a C-shaped spring.
In general, in one aspect, a method of integrally forming a glass seal includes providing a lid for a cell, forming a hole in the lid, disposing a post surrounded by an annular layer of glass within the hole and heating the cell until the glass seals to the lid.
In general, in one aspect, a method of providing power to a downhole tool includes providing a housing adapted to be mounted about an exterior circumference of the cylindrical member having a plurality of mutually engageable annular segments. At least one of the segments defines a chamber. The method also includes placing a cell for producing power within the chamber, mounting the plurality of annular segments about the cylindrical member and providing power to the tool from the cell.
Other advantages and features will become apparent from the following description and from the appended claims.